Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Sep 05 2025 12:31:12 AWUS01 KWNH 051231 FFGMPD AZZ000-NVZ000-CAZ000-051630- Mesoscale Precipitation Discussion 1048 NWS Weather Prediction Center College Park MD 830 AM EDT Fri Sep 05 2025 Areas affected...Lower Colorado River Valley (Western Arizona, Adj California)... Concerning...Heavy rainfall...Flash flooding possible Valid 051230Z - 051630Z SUMMARY...Localized flash flooding threat continues downstream of slowly weakening MCS/convective clusters within the Lower Colorado River Valley.=20 DISCUSSION...KESX and GOES-W 10.3um EIR show shrinking convective complex has had a resent uptick in convective vigor across central Mohave county. There was a typical weakening trend toward diurnal minimum, but the leading outflow boundary (combined with reinforcement from the northeastern dying convection) increased surface to boundary layer convergence as the cluster was reaching the nose of the Lower Colorado Valley where lingering unmixed, conditionally unstable air has been sitting through the overnight period. MUCIN has been below 25 J/kg and with some southerly weak flow intersecting the 30-45kt outflow has been sufficient to reactivate and break through the cap tapping some of the steeper profiles and 1500-2000 J/kg of ML/MUCAPE. Combine that with deeper available moisture in lowering elevation and inflow will continue to support intense sub-hourly rates and localized 1-1.25" totals. Most of the Hi-Res CAMs have been traditionally slow to the forward propagation of the cluster, reducing the moisture convergence but also delaying arrival to the reservoir of unstable air further south and have shown the erosion faster. However, recent RRFS solutions; though still too slow to reality of timing, do suggest continued southward propagation and longevity through the next few hours. Still, like any conditionally unstable air, the updraft strength will require the outflow's convergence to maintain, but current trends suggest this cluster may continue for a few more hours and the strength of rates will continue to pose sub-hourly FFG exceedance and localized flash flooding conditions along dry washes across the Lower Colorado Valley, mainly east of the River in Arizona. Of interest, but perhaps not reaching intensity required for inducing flash flooding; the rear-inflow jet continues to respond from NW to SE across south-central NV. Convergence along the western upstream edge has been similarly sufficient to tap the steeper mid-level lapse rates for scattered cells. These cells have favorable orientation for some weak training/repeating; but also are fairly elevated that evaporative loss may still keep overall rates/totals just below levels to produce flash flooding, except if they maintain/track through areas that received heavy rainfall overnight. Gallina ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!8aPH7a1SVnnQEXE9GCnjMwylxvLwnt0T0egP5wxPxB5Ft58ySvQIttC0BDGuTShqMw0b= v46Xr-E3SHgdw7QxcB1nyFY$ for graphic product... ATTN...WFO...FGZ...PSR...VEF... ATTN...RFC...RSA...STR...NWC... LAT...LON 35521375 35161322 34481290 33541266 33011326=20 33041421 33401453 34221475 34751481 35271456=20 35501422=20 =3D =3D =3D To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM. --- SBBSecho 3.28-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .